Optical bubble detection system

ABSTRACT

An optical sensor includes a sample cell through which a fluid flows, an optical sensor formed by an optical emitter and an optical detector. The sample cell and the optical sensor use light refraction to determine the presence and size of a bubble passing through the sample cell. A housing may also be included to provide better control over light refraction and to protect the optical sensor.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to systems for administering solutions topatients in such a manner as to decrease the risk that air bubbles willbe inadvertently provided to the patient. More specifically, the presentinvention relates to a system for optically detecting bubbles insolution being provided to a patient.

2. State of the Art

Parenteral and Enteral feeding systems are used to provide solutions topatients. In parenteral systems, solutions such as balanced salinesolutions are administered to the patient's circulatory system. Enteralfeeding systems are provided for patients who, for one reason oranother, are unable to eat for themselves.

One common concern with both parenteral and enteral feeding systems isthat it is undesirable for large quantities of air to be provided withthe solution. In enteral systems, excessive air may irritate thedigestive system of the patient and complicate other medical conditions.Additionally, the air can render the volumetric calculations of theenteral feeding pump inaccurate.

In parenteral applications, the risk can be much greater. While air in aparentral infusion line is undesirable, large quantities of air cancause serious problems in the vascular system. In extreme cases,excessive air can even cause death of the patient. Thus, it is criticalin parenteral application that air not be delivered to the patient'svascular system.

In addition to the health concerns posed by the air being released intothe patient's body, the presence of air in the parenteral or enteralfeeding tube also means that the desired solution is not being deliveredto the patient. Each cubic centimeter of air is a cubic centimeter ofenteral feeding solution, medication, etc. which is not delivered to thepatient. Without being able to detect the quantity of air passingthrough the system, the system is unable to accurately determine theactual amount of solution which has been delivered to the patient. Overa prolonged period of time, even modest amounts of air passing throughthe system can cause significant disparities in the amount of solutionthe system indicates to be delivered and the actual amount delivered.

There are numerous mechanisms available for detecting air in liquidpassing through a tube. Many of these mechanisms provide marginalaccuracy or are complex to use. Others, while relatively accurate,require considerably more power draw than is necessary. Yet other airdetectors do not provide an inherent integrity check to prevent failureof the sensor from giving erroneous information regarding air in theconduit.

While all of the above are disadvantageous, a principle disadvantage ofmost air detectors which are used in enteral feeding pumps and the likeis the cost. Most enteral feeding pumps utilize ultrasonic sensors tocheck for bubbles. Such sensors, however, can cost fifty times or morethe cost of an optical sensor.

Thus, there is a need for an improved sensor for determining thepresence of bubbles, which is less expensive, and which is easy tooperate.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved sensorfor detecting bubbles in a conduit;

It is another object of the present invention to provide such a sensorwhich is easy to make and use.

It is yet another object of the present invention to provide such asensor which utilizes refraction of light to determine the presence ofair within the conduit.

It is still another object of the present invention to provide such anoptical sensor which is relatively inexpensive.

The above and other objects of the invention are realized in specificillustrated embodiments of an optical air/liquid sensing system whichutilizes a sample cell. The sample cell has a pair of sidewalls whichrefract light into the liquid in the conduit at such an angle that thelight passes out of the sample cell in a first direction when no air ispresent in the conduit, and in a second direction when air is present inthe conduit.

The sample cell is disposed between an optical emitter and an opticaldetector. Light is emitted from the optical emitter and is refracted asit passes through the sample cell. The presence of air within the samplecell changes the refraction of light, thereby changing the lightreceived by the optical detector. It should be appreciated that, as usedherein, the term light is not limited to electromagnetic radiation inthe spectrum visible to humans. To the contrary, a preferred embodimentof the invention utilizes infrared radiation.

In accordance with one aspect of the present invention, the amount ofair in the conduit affects the amount of light refracted in the seconddirection. The amount of light refracted into the first direction versusthe amount refracted in the second direction indicates the relativeamount of air in the conduit.

In accordance with another aspect of the invention, the sample cell isconfigured and disposed to always allow some light to pass through thesample cell and to be received by the optical detector. If no light isdetected by the optical detector, the system is readily able todetermine that the system has failed.

In accordance with another aspect of the invention, the sample cell issituated so that all of the light emitted from the optical emitter doesnot reach the optical detector. Thus, if the optical detector indicatesthat nearly all of the light emitted from the optical detector has beenreceived, the optical sensor system can readily determine that thesample cell is not properly loaded between the optical emitter andoptical detector of the sensor.

In accordance with another aspect of the invention, the exterior of thesample cell is triangular. The shape of the sample cell regulates theflow of light through the sample cell and thereby directs light to theoptical detector depending on whether air is present in the conduit.

In accordance with still yet another aspect of the present invention, ahousing is provided and spaced apart from the sample cell by an airchannel. As with the shape of the sample cell, the housing helps todirect light through the sample cell at a desired angle to facilitatethe determination of whether air is present in the conduit in the samplecell.

Preferably, the housing is formed of a similar material to the samplecell and is disposed at an angle parallel to the sidewalls of the samplecell. This provides for the refraction of light at desired anglesthrough the sample cell.

In accordance with another aspect of the present invention, a samplecell container is provided with a channel disposed therein. Properlymounting a flexible tube in the channel causes the tube to form firstand second sidewalls which are disposed at desired angles to refractlight in one direction when a solution is present, and to refract lightin second direction, i.e. toward an optical signal detector, when theconduit is filled with air.

In a preferred embodiment of the invention, the sample cell hassidewalls which are disposed at an angle of between about 45 and 100degrees relative to one another are disposed at the same acute anglerelative to a plane extending from the optical signal emitter and theoptical signal detector. More preferably, the two sidewalls are disposedat an angle of 60 degrees from one another and are disposed at the samerelative acute angle from a horizontal or other plane passing throughthe sample cell from the optical signal emitter and the optical signaldetector. By same angle it is meant that each sidewall has a similaracute angle from the plane, although they are in opposite directions.

In accordance with another aspect of the invention, it has been foundthat the sample cell can be used to determine the presence of air solong as the sample cell wall is less than normal from the plane alongwhich the light is omitted. The closer the sample cell wall is tonormal, however, the further away the optical sensor components must befrom the sample cell wall. Additionally, the positions of the opticalsignal emitter and the optical signal detector can be adjusted to ensurelight is refracted to the optical sensor when air is present, but notwhen liquid is present, or vice versa.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the inventionwill become apparent from a consideration of the following detaileddescription presented in connection with the accompanying drawings inwhich:

FIG. 1 shows a perspective view of an optical sensing system made inaccordance with the principles of the present invention;

FIG. 2A shows a cross-sectional view of the optical sensing system shownin FIG. 1;

FIG. 2B shows the cross-section view of the optical sensing system shownin FIG. 2A with a conduit of the sample cell filled with liquid;

FIG. 2C shows the cross-sectional view of the optical sensing systemshown in FIG. 2A, wherein the conduit has an air bubble disposedtherein;

FIG. 2D shows the cross-sectional view of the optical sensing system ofFIG. 2 with an opaque solution therein;

FIG. 3 shows a bottom perspective view of an adaptor for use in enteralfeeding pumps having the sample cell of the optical sensor systemdisposed therein;

FIG. 3A shows a top perspective view, exploded view of the adaptor andan enteral feeding pump;

FIG. 4 shows a cross-sectional view of an alternate configuration of asample cell made in accordance with the principles of the presentinvention;

FIG. 5 shows a cross-sectional view of an yet another configuration of asample cell made in accordance with the principles of the presentinvention;

FIG. 6 shows a perspective view of a sample cell container made inaccordance with the principles of the present invention in an openposition;

FIG. 6A shows a perspective view of the sample cell container of FIG. 6in a closed position;

FIG. 6B shows a cross-sectional view of the sample cell container ofFIGS. 6 and 6B, forming a sample cell therein;

FIG. 7 shows a perspective view of yet another embodiment of a samplecell in accordance with the principles of the present invention;

FIG. 7A shows a cross-sectional view of the sample cell of FIG. 7;

FIG. 8 shows a cross-sectional view of yet another embodiment of thepresent invention; and

FIG. 9 shows still another embodiment of a sample cell and opticalsensor system made in accordance with the principles of the presentinvention.

DETAILED DESCRIPTION

Reference will now be made to the drawings in which the various elementsof the present invention will be given numeral designations and in whichthe invention will be discussed so as to enable one skilled in the artto make and use the invention. It is to be understood that the followingdescription is only exemplary of the principles of the presentinvention, and should not be viewed as narrowing the pending claims.

Referring to FIG. 1, there is shown a perspective view of an opticalsensor system, generally indicated at 100, made in accordance with theprinciples of the present invention. The optical sensor system 100includes an optical sensor, generally indicated at 104. The opticalsensor 104 has an optical emitter portion 108 which emits light, and anoptical detector portion 112 which detects light emitted by the opticaldetector and generates a voltage that is proportional to the amount oflight received. The optical emitter portion 108 and the optical detectorportion 112 define a cavity 116 through which the light travels betweenthe two portions. (Those of skill in the art will appreciate that theoptical sensor 104 can be made of a paired emitter and detector, orcould be formed from two discrete parts.)

The optical sensor 104 further includes a plurality of leads 120 whichare used to send and receive electrical signals from the enteral feedingpump with which the optical sensor is associated. Those skilled in theart will appreciate that optical sensors which function in such a mannerare inexpensive and readily available.

Positioned to extend through the cavity 116 in the optical sensor 104 isa sample cell 130. The sample cell 130 includes a sample cell wall 134which defines a conduit 138. In a presently preferred embodiment, thesample cell wall 134 defines a triangular conduit. Most preferably thesample cell wall 134 forms a conduit which, in cross-section, is aninverted equilateral triangle. The sample cell wall 134 also preferablyforms a base 142 disposed at the bottom tip of the triangle.

Disposed adjacent to and extending along the sample cell 130 is ahousing 150. The housing 150 has a base portion 154 which preferablyextends horizontally, a pair of sidewalls 158 which extend upwardly andoutwardly, and an upper flange portion 162. The respective sidewalls 158of the housing 150 preferably are disposed in parallel to the respectiveside walls 134 a and 134 b of the sample cell wall 134. Depending on theplastics used, the angle of the sidewalls 134 a, 134 b and 158 willpreferably be between 45 and 100 degrees. Most preferably, they aredisposed at an angle of 60 degrees from one another and from a planealong which light would flow uninterrupted between the optical signalemitter 108 and the optical signal detector 112.

The housing 150 and the sample cell 130 are spaced apart from oneanother and define an air chamber 170 therebetween. The housing 150serves several purposes. First, the housing 150 prevents water or otherliquids from getting into the cavity 116 where it could damage theoptical sensor 104. Second, the housing 150 is designed so that even ifwater were to fill the air chamber 170 between the housing and thesample cell 130, the flow-path of light indicating the presence ofliquid or air would be consistent.

Turning now to FIG. 2A, there is shown a cross-sectional view of thesample cell 130 disposed in cavity 116 between the optical emitter 108and the optical detector 112 of the optical sensor 104. The housing 150is disposed in parallel and spaced away from the sample chamber 130 toform the air chamber 170.

As shown, the sample cell 130 is preferably formed by a three partsample cell wall 134 defining a triangular conduit 138. Most preferably,the conduit has a cross-section which is an inverted equilateraltriangle. In such a configuration, the two sidewalls 134 a and 134 b ofthe sample cell wall 134 are offset from one another sixty degrees. Thetwo sidewalls are also offset from the horizontal plane 2A—2A at anangle of sixty degrees. The horizontal plane 2A—2A represents the planealong which light passing directly from the optical signal emitter 108to the optical signal detector 112 would pass.

It has been found that such an angular arrangement provides a light flowpattern which readily facilitates the determination if there is air inthe sample cell 130 and the relative amount of air present. As will beexplained in additional detail below, having the sidewalls disposed atcorresponding angles between 47-70 degrees and preferably 60 degreesallows light to be conveniently refracted in one direction if theconduit has liquid therein, and in a second direction, back toward theplane 2A—2A when the conduit is filled with air.

Disposed at the bottom of the sample cell 130 is a base portion 142which extends horizontally (i.e. parallel with the plane 2A—2A) a shortdistance, rather than forming a point similar to an inverted equilateraltriangle. The base portion 142 allows a certain amount of light to passthrough the sample cell 130 and to be received by the optical detector112 regardless of whether there is air or water in the conduit 138 ofthe sample cell. This forms an inherent integrity check, as the lack ofany detected signal will mean the optical emitter 108 is not working andthe optical sensor 104 must be replaced.

The housing 150 is positioned to both protect the optical sensor 104from being damaged by water, etc., and to assist in the flow of lightthrough the sample cell 130. As shown in FIG. 2B, the light from theoptical emitter 108 refracts as it passes into and out of the housing150. It refracts again as it passes into the sample cell wall 134 a.

If water or some other translucent solution is present in the conduit138, the water refracts to a very small degree as it passes from thesample cell wall 134 a into the liquid. This is because the refractionindex of the plastic which forms the sample cell wall 134 and therefraction index of the liquid is very similar.

Due to the similarities in the indices of refraction, the majority ofthe light will follow a generally straight path through the sample cell130 and will not return to the optical detector 112. Of course, a smallamount of the light will pass through the base portion 142 and will bedetected by the optical detector 112.

Turning now to FIG. 2C, there is shown a similar view to that of FIG.2A, but with the conduit 138 having a large air bubble disposed therein.The path of the light passing through the base 142 is the same i.e.along plane 2A—2A. The path of the remaining light is the same as FIG.2A until it reaches the conduit 138. Because air and plastic havesignificantly different indices of refraction, the light is bent so thatit travels generally horizontally across the conduit 138. When the lightimpacts the opposing portion of the sample cell wall 134 b, the light isrefracted downwardly. The light is again refracted as it enters andleaves the air chamber 170 and the housing 150, and is directed to theoptical detector 112. The amount of light which is received by theoptical detector 112 is roughly proportional to the size of the bubblein the conduit 138. Thus, a small bubble will create a small voltageincrease, while a large bubble will create a substantial voltageincrease. By monitoring the voltage produced by the optical sensor 104,the approximate size of the bubble can be determined. In practicalapplication in an enteral feeding context however, the number of airpresent signals generated over a given time will generally be moregermane. Thus, for example, ten air present signals will indicate thatthe solution has run dry or has a very high number of air bubbles.

Utilizing the configuration shown, a voltage reading of 0 indicates thesensor is malfunctioning, as some light should be passing through thebase portion 142 of the sample cell 130. A reading of 1 volt indicatesthat the sample cell is full of liquid and that the pump is deliveringthe indicated volume.

In contrast, a reading of 3-4 volts indicates that a much larger amountof light is being returned than expected, thereby indicating thepresence of a bubble. Where the voltage falls within this rangeindicates the size of the bubble. A reading of 5 volts indicates thatthe sample cell 130 and housing 150 are not properly mounted in theoptical sensor 104 and an alarm is sounded.

By monitoring the number of air bubble signals within a given amount oftime, the pump with which the sensor is used can adjust to ensure thatthe volume of solution delivered to the patient is accurate. If thenumber of air bubble signals is too high, the pump may shut down andgenerate an alarm indicating that the solution has run dry or is notproperly loaded.

Turning now to FIG. 2D, there is shown a cross-sectional view of thesample cell 130 having an opaque solution in the conduit 138. Becausethe solution is opaque, the light from the optical signal emitter 108 isblocked by the solution in the conduit 138, preventing it from beingdirected to the optical signal detector 112. Substantially the onlylight which does reach the optical signal detector 112 is that passingthrough the base portion 142. Thus, the optical signal detector 112receives the same signal regardless of whether the sample cell 130 isfilled with a transparent solution or an opaque solution. If a largebubble replaces the solution, whether transparent or opaque, the bubblewill cause the optical detector 112 to detect more light and indicatethe presence of the bubble.

Turning now to FIGS. 3 and 3A, there is shown, respectively, a bottomperspective view of an adaptor, generally indicated at 180, and theadaptor 180 in conjunction with a feeding pump 190. The adaptor 180includes a sample cell 130 of the optical sensor system 104. As shown inFIG. 3, the base portion 142 of the sample cell 130 is disposed on thebottom of the sample cell to allow some light to pass to the opticaldetector regardless of the contents of the sample cell.

The adaptor 180 enables the sample cell 130 to be conveniently mountedto the enteral feeding pump 190. As explained in additional detail inU.S. patent application Ser. No. 09/836,851 (which is expresslyincorporated herein), the pump generally includes a pair of channels 192and 194 which receive two sides 180 a and 180 b of the adaptor alongwith a working portion 196 of an infusion set which is attached atopposing ends to a first connector 184 and a second connector 188.

The sample cell 130 is formed in the first connector and is configuredto rest in one channel 192 in the enteral feeding pump 190. The housing150 (FIGS. 1 through 2D) is typically formed as a wall of the channel192 associated with the sample cell 130. The optical emitter 108 and theoptical detector 112 (not visible in FIG. 3A) are typically disposed onopposing sides of the channel 192 to function in the manner discussedabove.

The adaptor 180 also includes an anti-freeflow device 212 configured forpositioning in the other channel 194 of the pump 190. Typically, thesample cell 130 and the housing 150 will be disposed upstream, while theanti-freeflow device 212 is typically disposed downstream from a rotor204 which engages the working portion 196 of the infusion set and movesliquid through the sample cell 130 and past the anti-freeflow device 212by a plurality of rollers 206 which compress the working portion.

The adaptor 180 enables an infusion set to be quickly loaded into anenteral feeding pump. As the adaptor 180 is pushed into place, thesample cell 130 is automatically positioned between the optical signalemitter 108 and optical signal detector 112 housed in the pump 190. Ifthe pump 190 forms the housing 150, the sample cell 130 will alsopreferably be positioned away from the channel wall sufficiently todefine the air chamber.

If the adaptor 180 is not properly loaded in the pump 190, the amount oflight received by the optical signal detector 112 will fall outside apredetermined range. Typically, the optical signal detector 112 willreceive much more light than normal, thereby indicating the sample cell130 is not in place.

Turning now to FIG. 4, there is shown, a cross-sectional view of asample cell 230 made accordance with the principles of the presentinvention. While the sample cell 130 forming a conduit with across-section which is an inverted equilateral triangle is preferred,such a configuration is not required for the present invention tofunction properly. Thus, as shown in FIG. 4, the conduit 238 may have across-section which is diamond shaped. Because of the angled sidewalls234 a and 234 b, are angled between 45 and 100 degrees, and preferably60 degrees, from one another and are generally the same acute angle fromthe plane of the light emission, the light follows the same path asdiscussed above in FIGS. 2B and 2C, thereby enabling the sample cell 230to be used with the same housing 150 and sensor 104 configurationdiscussed above. Thus, as shown in FIG. 4, the air bubble in the conduit238 causes light to be refracted to the optical signal detector 112.

One advantage of the configuration shown in FIG. 4 is that the samplecell 230 will allow a greater amount of solution to flow through theconduit due to its increase in size. Such a configuration, however, mayincrease the likelihood of a partially filled conduit passing some airwhich is undetected.

FIG. 5 shows a cross-sectional view of another embodiment of a samplecell 250 in accordance with the principles of the present invention. Thesample cell 250 has a rounded top wall 254 to allow a greater amount ofsolution to flow through the conduit 258, while keeping the sidewalls254 a and 254 b disposed at an angle between about 45 and 100 degrees,and most preferably about 60 degrees, to provide the desired lightrefraction when air is present.

Because the most important aspects of the sample cell are the tangentialconfiguration of the sidewalls and the acute angle from the plane oflight transmission, those skilled in the art will appreciate thatnumerous other configurations could be used for forming the conduit. Forexample, the conduit could have a cross-sectional shape which forms anisosceles triangle, or could form a pentagon or some other shape. Inorder to properly refract light back to the optical emitter, however,the sidewalls should be separated by an angle between about 45 and 100degrees, and should have a similar acute angle relative to the plane oflight transmission.

Turning now to FIG. 6, there is shown a perspective view of yet anotherembodiment of a sample cell container, generally indicated at 300, madein accordance with the principles of the present invention. The samplecell container 300 has an upper portion 304 and a lower portion 308which are engageable one with another. The lower portion 308 has achannel 312 formed therein for receiving a flexible tube. The channel312 preferably has a base portion 316 for receiving the bottom of thetube and a center portion 320 which is formed by two opposing slopedsidewalls which are preferably sloped downwardly and inwardly toward thebase portion at an angle of between about 45 and 100 degrees from eachother and with a similar acute angle, i.e. each has the same relativeangle with respect to a horizontal plane so that the two wouldeventually intersect and have an angle between 45 and 100 degrees, andmost preferably about 60 degrees.

The channel 312 also has a top portion 322 which is configured toreceive a protrusion 330 disposed on the upper portion 304. When theupper portion 304 is closed, as shown in FIG. 6A, the protrusion 330extends down into the channel 312 to force the flexible tube disposedtherein into contact with the central portion 320 and base portion 316.This, in turn, causes the flexible tubing to conform to the shape of thechannel and form a tube which has a shape similar to that of the samplecell 130 shown in FIGS. 1-2D.

Turning now to FIG. 6B, there is shown a cross-sectional view of thesample cell container 300 with a flexible tube 340 disposed therein. Theprotrusion 330 has forced the flexible tube 340 downwardly, wherein thetube substantially conforms to the shape of the channel 312 and has abase portion 342, a central portion having two sidewalls 346 a and 346 bwhich are both disposed at the same angle from the horizontal plane,although in opposing directions, and a generally horizontal top portion346 c. In such a manner, the flexible tube 340 forms a sample cell whichdefines a conduit which is generally triangular. When disposed betweenan optical emitter and an optical detector, the sample cell formed bythe flexible tube 340 will function in substantially the same manner asthe sample cell 130 discussed above with respect to FIGS. 1 through 2D.

Those skilled in the art will appreciate that such a configuration isdesirable because it allows a conventional infusion set of an enteralfeeding pump to be adapted to provide a sample cell in accordance withthe principles of the present invention without having to cut the tubingor add an adaptor having a sample cell. Additionally, the sample cellcontainer 300 could be used repeatedly as infusion sets are replaced,thereby keeping cost to a minimum.

Turning now to FIGS. 7 and 7A, there is shown a perspective view and across-sectional view of a yet another embodiment of a sample cell of thepresent invention. The sample cell 350 forms a housing 354 having arectangular cross-section, and a triangular conduit therethrough. Aswith the previous embodiments, the conduit 358 has a cross-section whichis preferably an equilateral triangle, although other configurations,such as an isosceles triangle, diamond, pie, or other shape will work aswell provided that the light refraction is disposed to facilitatedifferent directions of light refraction depending on the contents ofthe conduit.

Those skilled in the art will appreciate that the configuration shown inFIGS. 7 and 7A are advantageous in that they can be used as a connectorfor conventional infusion sets for enteral feeding pumps to provideoptical bubble detection at minimal cost.

While the embodiments discussed above having two sloped sidewallsdisposed between 45 and 100 degrees, an in particular about 60 degrees,from one another are a preferred configuration for carrying out thepresent invention, it has been found that the angles can be much broaderwhile still obtaining some of the benefits of the present invention. Asshown in FIG. 8, there is shown a cross-sectional view of a sample cell,generally indicated at 400. The sample cell 400 is: formed by a cellwall 404 which has a first sidewall 404 a and the second sidewall 404 b.

An optical sensor system, generally indicated at 408 includes an opticalemitter 412 and an optical detector 416. The optical emitter 412 emitslight (i.e. electromagnetic radiation) along a plane 8A. The opticalsignal emitter 412 and the sample cell 400 are arranged so that thesidewall 404 a Is disposed at an angle less than normal to the plane 8A.As such, the sidewall 404 a causes the light to refract as it contactsthe outside of the sidewall.

If the sample cell 400 has clear liquid disposed therein, the lightundergoes minimal refraction as it passes out of the sidewall 404 a,through the liquid 424, and through the opposing sidewall 404 b asindicated by plane 8A′. Thus, the light does not reach the opticalsignal detector 416. Of course, if the liquid disposed in the samplecell 404 is opaque, the liquid will stop the light and prevent it frombeing received by the optical signal detector 416—giving the same resultas a clear liquid.

If an air bubble 424′ is disposed in the sample cell 400, the lighttraveling along plane 8A will be refracted both as it enters and exitsthe first sidewall 404 a, and typically as it enters and exits thesecond sidewall 404 b, so that the light follows plane 8A″ and reachesthe optical signal detector 416. Thus, even using a relatively smallangle in the sample cell wall 404, the light can be directed to theoptical signal sensor when air is present, and not when the sample cellis filled with liquid.

While the sample call 400 shown in FIG. 8 has a wall 404 a which is lessthan normal and a wall which is disposed substantially normal to theplane 8A, it will be appreciated that by moving the optical signalemitter 412 and/or the optical signal detector, a variety of differentwall configurations, including two less than normal, could be used.

Turning now to FIG. 9, there is shown yet another embodiment of a samplecell, generally indicated at 450. The sample cell 450 has a pair ofsidewalls 450 a and 450 b which are disposed slightly off 90 degreesfrom the plane 9A. The sidewalls 450 a and 450 b refract light in amanner similar to that discussed above. However, because the angle lessthan normal (i.e. less than 90 degrees) is so small, the optical signalemitter 462 and the optical signal detector 466 are spaced further fromthe sample cell 450.

When the light traveling along plane 9A impacts the sidewall 450 a it isrefracted. If relatively clear liquid is disposed in the sample cell450, the light follows a relatively straight line, plane 9A′ and doesnot reach the optical signal detector 466. If, however, a predeterminedamount of air is present in the sample cell 450, the light is refractedback toward the optical signal detector 466 as it passes from the firstsidewall 450 into the conduit 458 in the sample cell, from the conduitinto the second sidewall 454 b and from the second sidewall back intothe air between the sample cell and the optical signal detector. Thedistance of the optical signal emitter 462 and optical signal detector466 from the sample cell 450 exaggerates the amount of refraction byproviding more distance for the light to travel along the refractedplane.

Thus there is disclosed an improved optical bubble detector. Thoseskilled in the art will appreciate numerous modifications which can bemade to the embodiments and methods discussed herein without departingfrom the scope and spirit of the present invention. The appended claimsare intended to cover such modifications.

What is claimed is:
 1. A sample cell for monitoring the flow of aliquid, the sample cell comprising, a cell wall defining a conduit, theconduit having a triangular cross-section, and a base portion positionedadjacent the conduit and along the cell wall, the base portion extendingaway from the conduit and being configured for the passage of lighttherethrough without passing through the conduit.
 2. The sample cell formonitoring the flow of a liquid according to claim 1, wherein theconduit has a cross-sectional shape of an inverted equilateral triangle.3. The sample cell for monitoring the flow of a liquid according toclaim 1, wherein the cell wall has a generally triangular exterior. 4.The sample cell for monitoring flow of a fluid according to claim 3,wherein the cell wall forms an inverted equilateral triangle.
 5. Thesample cell for monitoring flow of a fluid according to claim 4, whereinthe base portion is positioned at the bottom of the equilateraltriangle.
 6. The sample cell according to claim 5, wherein sample cellis configured for light to be directed at the sample cell along a path,and wherein at least one side of the base portion forms a wallperpendicular to said path.
 7. The sample cell according to claim 1,wherein the base portion extends in a direction transverse to the cellwalls defining the conduit.
 8. The sample cell according to claim 1,wherein the cell wall has a first wall and a second wall disposed at anangle of between 45 and 100 degrees from one another, and wherein thebase portion extends tangentially from both sidewalls.
 9. A device formonitoring fluids comprising: a sample cell having a cell wall defininga conduit, the cell wall having first and second sidewalls disposedtangentially to ane another, and a housing disposed adjacent to, butspaced apart from the sample cell.
 10. The device according to claim 6,wherein the housing has a pair of sidewalls disposed in parallel to thesidewalls of the sample cell.
 11. The device according to claim 10,wherein the sidewalls of the sample cell and the sidewalls of thehousing are disposed at an angle of between about 47 and 70 degreesrelative to one another.
 12. The device according to claim 11, whereinthe sidewalls of the sample cell are offset from one another at an angleof about 60 degrees.
 13. The device according to claim 10, wherein thesidewalls of the sample cell and the sidewalls are disposed at an angleof about 60 degrees from a horizontal plane.
 14. The device according toclaim 9, wherein the housing is spaced from the sample cell to define anair chamber.
 15. The device according to claim 9, wherein the housingfurther comprises an upper flange portion.
 16. The device according toclaim 9, wherein the housing further comprises a generally horizontalbase portion.
 17. The device according to claim 16, wherein the housingis formed as a channel wall of an enteral feeding pump.
 18. The deviceaccording to claim 9, wherein the device further comprises ananti-freeflow mechanism.
 19. The device according to claim 9, whereinthe device further comprises a cartridge having a tube attached thereto.20. The device according to claim 9, further comprising an opticalemitter and an optical detector.
 21. The device according to claim 20,wherein the sample cell has a base portion which is not intersected bythe conduit of the sample cell, and which is disposed between theoptical emitter and the optical detector for allowing light to betransmitted from the optical emitter to the optical detector regardlessof contents in the conduit.
 22. The device according to claim 20,wherein the housing has a base portion which is disposed between theoptical emitter and the optical detector for allowing light to betransmitted from the optical emitter to the optical detector.
 23. Thedevice according to claim 20, wherein the sample cell and the housingeach have sidewalls disposed at an angle of about 60 degrees from aplane extending between the optical emitter and the optical detector.24. A device for monitoring the flow of a liquid, the device comprising:a sample cell having a cell wall with at least two sidewalls disposed atan angle of between 45 and 100 degrees from one another and defining aconduit; a housing disposed adjacent to but spaced apart from the samplecell so as to define an air chamber between the housing and the samplecell.
 25. The device according to claim 24, further comprising anoptical emitter and an optical detector disposed on opposing sides ofthe housing.
 26. The device according to claim 24, wherein the housinghas at least two sidewalls disposed substantially parallel to thesidewalls of the cell wall.
 27. The device according to claim 24,consisting of a single optical detector.
 28. The device according toclaim 27, wherein the device comprises means for determining if thesample cell is properly positioned in the housing, means for determiningif the optical emitter is working, and means for determining if there isair or liquid in the conduit.
 29. The device according to claim 28,wherein the means for determining if the sample cell is properlypositioned in the housing, the means for determining if the opticalemitter is working, and the means for determining if there is air orliquid in the conduit is the single optical emitter.
 30. A bubbledetection system comprising the sample cell according to claim 1, andfurther comprising an optical signal emitter and an optical signaldetector.
 31. The device according to claim 30, wherein the base portionof the sample cell is disposed to transmit light between the opticalemitter and the optical detector uninterrupted by contents of theconduit.
 32. A sample cell for use in monitoring of air bubbles in aninfusion set, the sample cell comprising a conduit and a base portionextending from the sample cell configured to allow light to passtherethrough regardless of contents of the conduit.
 33. The sample cellof claim 32, wherein the sample cell comprises first and secondsidewalls disposed tangentially to one another at an angle of betweenabout 45 to 100 degrees.
 34. The sample cell according to claim 33,wherein the base portion is configured to allow light to passtherethrough generally horizontally with minimal refraction.
 35. An airbubble sensor system comprising a sample cell in accordance with claim32, further comprising an optical signal emitter and an optical signaldetector.
 36. The air bubble sensor system according to claim 35,wherein the optical signal emitter is disposed adjacent the firstsidewall and wherein the optical signal detector is disposed adjacentthe second sidewall.
 37. The air bubble sensor system according to claim36, wherein a light emission plane extends from the optical signalemitter to the optical signal detector, and wherein each sidewall has anacute angle from the light emission plane which is substantially thesame as the acute angle from the light emission plane of the othersidewall.
 38. The air bubble sensor system according to claim 37,wherein both the first and second sidewalls are disposed 60 degrees fromthe light emission plane.
 39. The air bubble sensor system according toclaim 35, further comprising a housing disposed adjacent to the samplecell.
 40. The air bubble sensor system according to claim 39, whereinthe housing is disposed between the sample cell and the optical signalemitter and the optical signal sensor.
 41. The air bubble sensor systemaccording to claim 40, wherein the housing has a sidewall disposedgenerally parallel to the first sidewall of the sample cell and a secondsidewall disposed generally parallel to the second sidewall of thesample cell.
 42. The sample cell of claim 32, wherein the sample celldefines a conduit, the conduit having a triangular cross-section. 43.The sample cell according to claim 32, wherein the sample cell defines aconduit and wherein the conduit has a generally diamond shapedcross-section.
 44. A method for monitoring a conduit for supplying aliquid, the method comprising: positioning the conduit between anoptical emitter and an optical detector; emitting a signal from theoptical emitter to the optical detector; and utilizing the opticalsignal received by the optical detector to determine at least two of thegroup consisting the presence of the conduit; the presence of air in theconduit; and that optical emitter is sending the optical signal.
 45. Themethod according to claim 44, wherein the method comprises determiningthat the conduit is in place by detecting an amount of the opticalsignal less than an amount detected when the conduit is not in place.46. The method according to claim 44, wherein the method comprises,detecting air in the conduit by detecting an amount of the opticalsignal received by the optical detector which is greater than the amountreceived when there is liquid in the conduit.
 47. The method accordingto claim 44, wherein confirmation that the optical emitter is sending anoptical signal is determined by the optical detector receiving a portionof the optical signal regardless of whether the conduit is in place andregardless of whether the conduit has air therein.
 48. The methodaccording to claim 47, wherein the method comprises passing a portion ofthe signal through a base portion formed by a wall defining the conduit,the base portion being configured to allow light to pass therethroughwith minimal refraction regardless of the contents of the conduit. 49.The method according to claim 44, wherein the method comprisespositioning the optical emitter and the optical detector so that theoptical detector receives less optical signal when the conduit is inplace than when the conduit is not in place, and less optical signalwhen the conduit is filled with liquid than when the conduit is filledwith air.
 50. The method according to claim 49, wherein the methodcomprises positioning the conduit, the optical detector and the opticalsensor, so that the optical detector always senses some optical signalfrom the optical emitter when the optical emitter is working.
 51. Themethod according to claim 44, wherein the method comprises using asingle optical detector and optical emitter to determine presence of theconduit, whether the conduit has air therein, and whether the opticalemitting is emitting optical signals.
 52. A method for monitoring airbubbles in an infusion set, the method comprising; selecting a samplecell having a first sidewall and a second sidewall, the first and secondsidewall being disposed at an angle relative to one another betweenabout 45 and 100 degrees and having a conduit formed therein;transmitting light from an optical signal emitter toward an opticalsignal detector and into the sample cell and refracting a greater amountof light toward the optical signal detector if air is present in theconduit; and directing light through the sample cell such that theoptical detector always receives light if the optical emitter isworking.
 53. The method according to claim 52, wherein the methodcomprises; more specifically, selecting a sample cell having sidewallswhich are offset from one another at an angle of about 60 degrees. 54.The method according to claim 52, wherein the method comprises passingsome light from the optical signal emitter to optical signal detectorthrough the sample cell, but not through the conduit.
 55. The methodaccording to claim 52, wherein the method further comprises disposing ahousing adjacent the sample cell for refracting light.
 56. A method fordetecting bubbles in a sample cell, the method comprising; selecting asample cell having a conduit, an optical signal emitter and an opticalsignal detector; determining whether the sample cell is properlypositioned between the optical signal emitter and the optical signaldetector by the amount of light detected by the optical signal detector;and causing different amounts of light to be refracted towards theoptical signal detector depending, on whether the conduit is filled withair or is filled with a liquid.
 57. The method according to claim 56,wherein the method comprises transmitting the light along a plane andrefracting the light with a sample cell wall disposed at an angle lessthan normal to the plane.
 58. The method according to claim 56, whereinthe method comprises stopping the transmission of light with an opaqueliquid in the sample cell.
 59. The method according to claim 58, whereinthe method comprises directing some light to the optical signal detectorregardless of the contents of the sample cell.
 60. A method for forminga sample cell from flexible tubing the method comprising: selecting asample cell container having a channel formed therein defining a pair ofsidewalls sloping toward one another and being disposed at an angleoffset from each other of between about 45 and 100 degrees; and engagingthe flexible tube with the pair of sidewalls to deform the flexible tubeso that the flexible tube has sidewalls disposed generally parallel tothe pair of sidewalls of the sample cell container, and so that a baseportion is formed for passing light therethrough with minimalrefraction.
 61. A sample cell container for forming a sample cell from apiece of flexible tubing, the sample cell container comprising; a lowerportion having a channel formed therein, the channel having a pair ofinwardly sloping sidewalls disposed tangentially to one another at anangle of between about 45 and 100 degrees, and a base portion formed ata bottom end of the inwardly sloping sidewalls; and an upper portionhaving a protrusion for nesting into the lower portion to deform theflexible tubing.
 62. A method for determining the presence of air in asample cell, the method comprising; selecting a sample cell having asidewall; directing light from an optical emitter along a plane towardthe sample cell such that the sidewall of the sample cell is at an angleof less than normal from the plane; and selectively refracting the lightthrough the sample cell so that the light is directed to an opticaldetector when the sample cell is substantially filled with air;directing a portion of the light through the sample cell with minimalrefraction to indicate that the light has been emitted into the samplecell.
 63. The method according to claim 59, wherein the sample cell hasa pair of sidewalls through which the light passes, and wherein thesidewalls are angled away from each other at an angle of 45 to 110degrees.
 64. The method according to claim 59, wherein the methodcomprises positioning the optical sensors to maximize detection ofrefracted light.
 65. A method for monitoring for bubbles, the methodcomprising; selecting a sample cell having a first sidewall and a secondsidewall on opposite sides of a conduit; passing a portion of the lightthrough the sample cell so that said portion is subject to minimalrefraction regardless of the contents of the conduit; and refractinglight through the first sidewall, the conduit and the second sidewallsuch that the light reaches an optical signal detector when the samplecell has an air bubble disposed therein, and so that substantially noneof the light passing through the conduit reaches the optical detectorwhen the sample cell is filled with liquid.
 66. The method according toclaim 65, wherein the method comprises, emitting light along a plane,and disposing the first sidewall at an angle less than normal to theplane.
 67. The method according to claim 65, wherein the methodcomprises selecting a sample cell with the first and second sidewallsdisposed at an angle between about 45 and 100 degrees from one another.68. The method according to claim 65, wherein the method furthercomprises using a single sensor to determine whether light has beenemitted and to determine if the sample cell has air herein.
 69. Themethod according to claim 68, wherein the method further comprisesrefracting a different amount of light to said sensor when the samplecell is in a proper position for monitoring.